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PETROLEUM SYSTEMS

The elements and processes of a petroleum system explained in brief.

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PETROLEUM SYSTEMS

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  1. PETROLEUM SYSTEMS BY: ONWUAZOMBE TOBECHUKWU

  2. OUTLINE • Introduction to Petroleum Systems concept • Elements and processes of a Petroleum System • Source rocks and petroleum generation • Migration • Reservoir rocks • Traps and petroleum accumulation • Seal/Cap rock • Evolution of a petroleum system in a basin • Conclusion • Reference.

  3. THE PETROLEUM SYSTEMS CONCEPT Petroleum describes a compound that includes high concentrations of any of hydrocarbon gas, condensates, crude oils and natural bitumen. • The petroleum system concept is a unifying concept that encompasses all of the disparate elements of petroleum geology. • A petroleum system encompasses a pod of active source rock and all genetically related oil and gas accumulations. • It includes all the geologic elements and processes that are essential if an oil and gas accumulation is to exist. A system is a defined as a region in space chosen for study.

  4. Elements and processes of a petroleum system • ELEMENTS AND PROCESSES • The essential elements of a petroleum system include the following: • Source rock • Reservoir rock • Seal rock • Overburden rock • Petroleum systems have two processes: • Trap formation • Generation-migration-accumulation of hydrocarbons. • A sedimentary basin is a depression filled with sedimentary rocks. • The essential elements of a petroleum system are deposited in a sedimentary basin. • The essential elements and processes must be correctly placed in time and space so that organic matter included in source rock can be converted into petroleum accumulations. • A petroleum system exists wherever all the essential elements and processes are known to occur .

  5. The age of a system is the time required for the process of generation-migration-accumulation of hydrocarbon. • The geographic extent of a petroleum system the area over which the system is known to occur. • The stratigraphic extent is the span of lithological units from below the pod of active source rock to the top of overburden rock. • The size of a petroleum system is the total volume of all recoverable hydrocarbon tat originated from a single pod of active source rock.

  6. SOURCE ROCK AND PETROLEUM GENERATION • A rock rich in organic matter which if heated sufficiently, will generate oil or gas. • Fine-grained sediments of both siliciclastic and carbonate compositions are the principal source rocks of petroleum. • The petroleum-generating potential of a source rock is directly related to its volume, organic richness and thermal maturity. • Organic material are more likely to be preserved under low oxygen condition. • Increase in heat due to great burial depths cause organic matter to transform into insoluble organic matter known as kerogen. • Further heating, converts the kerogen, yielding bitumen and petroleum. • Total Organic Carbon (TOC) measurements determines if a rock has sufficient organic matter to be considered a source rock. • Typical source rock, usually shale or limestone, contain about 1% organic matter and at least 0.5% TOC.

  7. MIGRATION TYPES AND MECHANISMS Migration: This is the movement of petroleum from the source via carrier beds to the reservoir rocks. Primary migration Secondary migration

  8. RESERVOIR ROCKS AND TYPES • Clastic Reservoirs • Consolidated and unconsolidated sands. • Porosity is determined mainly by packing of grains. • Permeability is determined mainly by grain size and packing, connectivity and shale content. • Fractures may be present. • Carbonate Reservoirs • Carbonates (limestone and dolomite) normally have a very irregular structure. • Porosity is determined by shells, e.t.c and by depositional and post-depositional events. • Permeability is determined by deposition and post-depositional events, fractures. • Fractures may be very important in carbonate reservoirs. A petroleum reservoir is a sub-surface pool of hydrocarbons contained in porous or fractured rock formations. It must be porous and permeable.

  9. RESERVOIR ROCK PROPERTIES • Basic Reservoir Rock Properties • Porosity: This is the ratio of pore volume to the bulk volume of a rock sample. • Permeability: This is a measure of the capacity of a rock pore system to transmit fluid. • Water Saturation: This is the volume of water contained in the pore volume of rock. The remainder of the pore volume is, by definition, occupied by hydrocarbons.

  10. TRAPS • TRAPS • A trap is a configuration of rocks suitable for containing hydrocarbon and sealed by a relatively impermeable formation through which hydrocarbon will not migrate. • A trap aids accumulation of hydrocarbon in commercial quantities. • It could be structural or stratigraphic .

  11. TYPES OF TRAPS • Structural Traps: • Hydrocarbon traps that form in geologic structures such as faults and folds. • Sratigraphic Traps: • Hydrocarbon traps that results from changes in rock type or pinch outs, unconformities, or other sedimentary features such as reefs or buildups.

  12. SEAL/CAP ROCK • A cap rock or seal is a relatively impermeable rock that serves as a barrier between fluids and other rocks. • Buoyant, migrating fluids remain trapped in the reservoir by the cap rock unless deformation or erosion breeches the seal. • Salt, shale and anhydrite commonly have excellent sealing properties.

  13. EVOLUTION OF A PETROLEUM SYSTEM IN A BASIN This chart relates the timing relationship between the essential elements of a petroleum system and processes.

  14. CONCLUSION • The principal limit to petroleum abundance in every petroleum system is the ability of the source rock to provide a sufficient charge to associated carrier beds. • Appropriate relative timing of formation of the elements and processes of a petroleum system are necessary for hydrocarbon to accumulate and be preserved. • The petroleum system concept is a reliable/logical way to judge and describe the potential and exploration risks of undrilled prospects, plays and basins.

  15. reference • Vincelette, R.R., and W.E. Chittum, 1981, Exploration for oil accumulations in Entrada Sandstone, San Juan basin, New Mexico: AAPG Bulletin, vol. 65, p. 2546–2570. • D.H. Welte B. Horsfield D.R. Baker (Eds.) Petroleum and Basin Evolution Insights from Petroleum Geochemistry, Geology and Basin Modeling. • Petroleum systems by Leslie B. Magon and Edward A. Beaumont. • Petroleum Geoscience From Sedimentary Environments to Rock Physics knut Bjorlykke.

  16. THANK YOU

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